Saurauia, related to Actinidia, the Chinese gooseberry or kiwi-fruit genus, is a group of treelets of small to medium-size trees with an amphi-Pacific distribution, found in the South, Eastern and Southeast Asian regions, as well as parts of tropical America. Its richest representation is in the Malay Archipelago, where landscapes are highly varied in geology and topography, and populations are separated and differentiated on the very many islands. There, the species of Borneo have held fascination for great botanists of the past, but there has never been a collective account of this genus for theis iconic tropical island, where much of the plant life has remained little documented. For the first time, Borneo's Saurauia species are specially assessed, enumerating 85 species that include 62 newly described in this monograph. Emerging knowledge of rainforest trees such as Saurauia grant us a better understanding of the flora, revealing how the diversity may correlate with terrain, geology, vegetation across Borneo, and even helping us gauge the effectiveness of the conservation areas we have set up. This work exemplifies the intricacies of rainforest botany in recognising species and related groups (constructing a 'taxonomy'), considering aspects of biology that may have brought on the perceived patterns of biodiversity, and providing a first look at how this rainforest plant genus has responded in evolutionary and ecological terms to landform and habitat in Borneo.